DOC PREVIEW
UW-Madison G 777 - Research Paper

This preview shows page 1-2 out of 6 pages.

Save
View full document
View full document
Premium Document
Do you want full access? Go Premium and unlock all 6 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 6 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 6 pages.
Access to all documents
Download any document
Ad free experience

Unformatted text preview:

PHYSICALREVIEW 8VOLUME46,NUMBER1515OCTOBER1992-ISoft-x-ray-emissionstudies ofbulkFe3Si,FeSi,andFeSiz,andimplantediron silicidesJ. J.Jia,T.A.Callcott,W.L.O'Brien,andQ.Y.DongUniversityofTennessee, Knoxviile,Tennessee37996D.R. MuellerandD. L. EdererRational InstituteofStandards andTechnology,Gaithersburg,Maryland20899Z. TanandJ.I.BudnickUniversityofConnecticut,Storrs,Connecticut 06269(Received 27April1992)Bulk ironsilicidesandimplantediron silicideshave been studiedbysoft-x-rayemission(SXE)spec-troscopy.The SiL23emissionspectraof thesematerials are measured. For bulksilicides,thesespectraprovideameasure ofs-andd-type partial densityof states(PDOS) localized on the Si sites. Wecomparethemwithavailable band-structurecalculationsandalso withphotoemission measurements.Forim-plantedsystems,the SiL»emissionspectra provideuseful informationaboutthesilicideformationpro-cess withthe variationofimplantdoses.I.INTRODUCTIONInagreatnumber ofstudies'conductedon thetransition-metal(TM)silicides andmetal-siliconinter-faces,iron silicides have receivedfarless attention thancobalt andnickel silicides.Onlyasmall number ofelec-tronic structure studieshave beenperformedon ironsili-cides.Partly,this is duetothe lowertechnologicalpo-tential of iron silicides atpresent comparedwitheitherCoor Nisilicides,andpartlyit is due to thecomplexcrystalstructure of these materials. Yetiron silicideshaveveryinterestingelectronic andmagnetic properties.A morecomprehensive understandingoftheir electronicstructurescertainlywillhelptoexploretheseproperties.Oneof the threepurephasebulk Fesilicides,FeSi2isagoodsemiconductor andshowspotentialuseincombin-ingsilicon-baseddigital technologywith new optoelect-ronic devices.Another,Fe3Si,has drawn considerableinterestdue to thesiteoccupationpreferenceofsubstitu-tionaltransition-metalimpuritiesin thismaterial. But ithasbeen studiedmostlybynuclearmagneticresonance(NMR)and neutronscatteringtechniques.The magnet-icpropertiesandstructural stabilityof thethird, FeSi,arealsoveryinteresting.A clearpictureof itselectronicstructureandchemicalbondingisneeded tofullyunder-stand theseproperties.However,ourknowledgeofthesematerialsis stillincompleteasfar astheelectronicstruc-ture andchemicalbondingareconcerned.We havemadesoft-x-ray-emission(SXE)measurementsonthesematerialsin order togainmore experimentalinformationon thefilled bandsofthese compounds.SXEspectrosco-pyisaprovenmethod ininvestigatingthe bulkelectronicstructuresof solidmaterials.Ourpreviousstudies'havedemonstratedtheusefulnessofSXEspectroscopyinstudyingbulk silicidesandimplantedsilicides.Inpartic-ular,thes-andd-likepartialdensityofstatesofthevalence electronslocalized onSi sitescan be effectivelystudiedbythis method.Inthispaper,wewillpresentthe SiL23emission spec-tra of these bulk Fe silicides and also of someiron-implantedsiliconsamples.In SXEspectroscopy,ener-geticelectrons orphotonsareused togeneratevacanciesinthe core levels ofatoms withinthespecimen.Soft xraysareemittedas valenceelectronsradiativelyrecom-bine with thecore-levelvacancies. Theenergydistribu-tionofthesephotonsare detected andanalyzed,whichprovidesinformationaboutthe filled valence orconduc-tion bandsofthematerialsstudied.Because thespectraaregeneratedinradiative transitionsto alocalized corehole,thespectroscopyischemicallyselective and pro-vides a localdensityof states(LDOS)for each element ofacomplexsolid. Inaddition,the radiative transitionsobeythedipoleselection rule forangularmomentum sothat SXEspectra formallyrepresentangular-momentum-selectedpartial densityofstates(PDOS).Also,formostoperatingconditions,bothexcitation andescapedistancesaresufficientlygreatso thatSXE spec-troscopyis a bulkprobewhichisrelativelyinsensitivetosurface conditions.Bymeasuringthe SiL23emissionspectraofironsili-cides,thelocal s anddLPDOS'sfor the Si sites can beeffectivelyprobedbythismethod. Thisinformationisnot availablefromphotoemissionmeasurements duetothedominance of the Fe delectrons in photoemissionspectra.We will discuss theinvolvement ofsilicon selec-tronsinbondingandcompareourresultswithavailablecalculations and photoemissionresults.Generalagree-ment is found betweenourspectrumonFeSi2andtheoretical calculations aswellaspreviousexperimentalresults.Somecomparisonscan alsobemadewithlessde-tailedcalculationsavailable forFe3Si.Nodetailedband-structure calculationswithprojectedLPDOSexist intheliteraturefor FeSi. However,somecleartrendscan beidentifiedingoingfrom iron-poortoiron-richcom-4694461992TheAmericanPhysicalSociety46SOFT-X-RAY-EMISSIONSTUDIES OFBULKFe3Si,FeSi,...poundsthatgiveinformationabout the evolutionofbondingin these materials.II. EXPERIMENTl 1 I(IIIl(I I IIfI Il I(II I I(Ii yy(pggFe SiThebulk FeSiandFeSi2 sampleswerepreparedbycompressingcommercially obtainedpowdersintopellets.Thepowdershavecrystallitesvisiblylargeenoughtorepresentthebulkproperties.TheFe3Sisampleisasin-glecrystalpreparedbyarcmelting.Itscompositionandcrystalstructure werecheckedbyx-rayscattering.Theiron-implantedsampleswerepreparedbyuniformlyim-plantingpolishedsilicon(100)wafers.Ascanningbeamof150-keVFe+ionswas used forimplantationwithsub-stratetemperature maintainedat about350'Cin avacu-um of 10 Torr.Thesampleholder was surroundedbya liquid-nitrogentrapandwarmedbya heaterwithtem-peraturesmonitored and stabilizedduringthe implanta-tion.Thesampleswestudied here haveimplantationdosesof 5 X10',7 X10',and 1X10'Fe/cm .SXEmeasurementswere carried out on our high-efficiencySXEspectrometerinstalledat the NationalSynchrotronLightSource,Brookhaven NationalLabora-tory.Spectrometerand detectorhave been describedelsewhere.''"Our measurements were conductedwith a600-lines/mmgratinganda100-p,minputslit.Instru-mental resolution isestimatedtobebetter than0.2eVataphotonenergyof 100 eV. Measurements were madeinan UHVchamber at apressureof 5X10Torr.Emis-sionwasexcitedbya100-pA,3-keVelectron beamfo-cusedto a1-mmspot.Thesampleswereplacedonaholderlocated3or 4mmawayfrom the entrance slit ofthespectrometer.Electrons were incident on thesampleatanangleof30'fromthesamplenormal,andthetake-offanglefor x-rayswas50'.Thespectrawere correctedforthe nonuniformdetectorresponseandastigmaticde-formationin thenondispersiondirection.Completespec-tra wereassembled fromsegmentstaken at successive po-sitionsalongthe Rowland circle. Eachsegmentcoversroughly15A in the siliconLemissionrange.Brems-strahlungbackgroundinducedin electron excitation isfitted as astraightlineand subtracted from thespectra.Forthe3-keVelectronexcitation, weestimate


View Full Document

UW-Madison G 777 - Research Paper

Documents in this Course
Load more
Download Research Paper
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Research Paper and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Research Paper 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?